Before he died, Gideon Cahill left seven Clues to his eldest son, Luke. These seven Clues combined make the Lucian Serum. The Lucian Serum gives the drinker the enhanced abilites of the Lucian Branch of Cahills. These abilites include: espionage, strategy, leadership, secrecy, sabotage, lying, and stealth.
Iron Solute is the first Clue mentioned in the series. It was found by Amy Cahill. She also found the Lucian Serum. The serum was stolen by Ian Kabra and later drank by Isabel and maybe Vikram. The Clue, however, was still with Amy and Dan. The Clue Calcium is not mentioned in the books. The Clue is currently stored in Area 51, a secret Lucian Stronghold. Whenever the locals try to discover what was in there, the Lucians seize them and make it look like it was an alien abduction. It is possible that Eisenhower Holt has this Clue. The Clue Salt is also not mentioned in the books. It was stolen by Walter Raleigh, a Janus. After the Lucians found out about this they hunted Raleigh, arrested him, but the Clue was back in the Tower of London. Clover is another Clue not mentioned in the books. The Lucians hid this Clue in Fort Knox. They also stored gold to throw rivals off track. Blood is yet another Clue not mentioned in the books. The Lucians paid Gustave Eiffel 10,000,000 francs to construct the Statue of Liberty and the Eiffel Tower so they could swap the Clue's location, which they did so every 10 years. The Tomas tried to find the Clue but failed. Amber is the second Lucian Clue to be mentioned in the books. It was hidden in the Amber Room. Dan and Amy found it with some help from NRR a.k.a Anastasia's daughter, Nataliya. Irina, Ian and Natalie failed to protect this Clue. The last Lucian Clue is Mint. Josephine Baker stole the Clue on its way out of France. Then she hid it in Morocco.